This disclosure relates to acoustic sensors and methods of making and using such acoustic sensors in various tools, including acoustic logging tools.
Typically, downhole acoustic logging tools, which are used for estimating formation properties, include one or more acoustic transmitters or sources and a number of acoustic receivers. The transmitters induce acoustic energy into the formation surrounding the wellbore. The acoustic signals are reflected by interfaces associated with the wellbore and formation. The reflected acoustic signals are detected by the receivers in the logging tool and processed to provide estimates of one or more properties of the formation. A large number of acoustic sensors utilize piezoelectric ceramic elements as active elements. Some downhole tools utilize as many as 24 acoustic receivers. Seismic spreads use several thousand acoustic receivers for obtaining seismic data. The piezoelectric ceramic elements are relatively large and expensive. The present disclosure provides acoustic and vibration sensors that utilize quantum tunneling composites as active elements.